As is well known, an amplifier is a device that receives an input and applies a defined gain in order to produce an output that is greater than the input. For example, a voltage amplifier may receive a 10V input and produce an output of 20V, if the voltage amplifier has a gain of two. Amplifiers are able to apply the gain to produce an output up to a certain value. For example, a voltage amplifier can produce an output up to a value of the operational voltage applied to the amplifier. That is, a voltage amplifier with an operational voltage of 15V and a gain of three can produce the desired output as long as the input does not exceed 5V. If the voltage amplifier receives an input voltage of 6V it would attempt to produce an output of 18V, which is above the maximum that this voltage amplifier can produce. Therefore, the voltage amplifier would not have the potential to drive the load to the desired voltage. Thus, when designing a device utilizing an amplifier, assurances should be made that the amplifier can handle the maximum input that will be received. That is, if the typical range of input voltages is 3-5V but a peak voltage of between 6-8V is possible, the amplifier should be capable of handling an 8V input.
Amplifiers work best if they are producing outputs that are near the maximum output that the amplifier can handle. That is, a 15V amplifier works most efficiently when producing outputs around 15V. However, the typical outputs of a 15V amplifier are probably much lower since the 15V operating voltage (i.e., maximum output) was selected to handle peak input voltages. For example, the maximum input voltage (peak voltage) for a 15V amplifier with a gain of three is 5V, and a typical input voltage may be in the range of 1-3V. An example 15V amplifier is illustrated in FIG. 1. A voltage supply V.sub.s is connected to the amplifier A. The amplifier A is powered by an operational voltage of 15V. The gain of the amplifier A is three as defined by resistors R1 and R2. The output voltage V.sub.o of the amplifier A is applied to the load R.sub.L. As the chart depicts the typical range of voltage inputs to the amplifier A from the voltage supply V.sub.s is between 1-3V so that the typical output voltage V.sub.o is between 3-9V. Therefore, the output voltage V.sub.o ranges between 20-60% of the peak output potential for the typical input. Thus, the amplifier A is typically very inefficient. FIG. 1 depicts the amplifier A receiving a peak voltage from the voltage source V.sub.s at time t7, at which time the amplifier A is at 100% efficiency. The amplifier A runs at peak efficiency only at the periods of time when peak input voltages are being received by the amplifier A.
Thus, an inherent problem associated with standard amplifiers is the conflict between the desirability of providing large output potentials and the undesirability of providing lower potentials through a large potential drop. One solution proposed is to provide separate amplifiers which each operate efficiently within a range. One amplifier would be designed to handle the typical inputs, while the other amplifier would be designed to handle the peak inputs. Switching between these two amplifiers would provide both efficiency and the capability of handling peak inputs. However, this type of dual amplifier has seldom been utilized because a complex switching means is required. For example, as illustrated in FIG. 2, a switching circuit would be required to receive the input voltage and make a determination of which of the two amplifiers the voltage should be applied to.
Thus, there is a need for an amplifier that provides high efficiency and high potential capability that does not require a complex switching mechanism.